Polypivalolactone is a well known thermoplastic material. Methods for its synthesis are described, for example, in U.S. Pat. Nos. 3,268,486, 3,471,456, 3,669,940 and 3,773,726 which patents are incorporated herein by reference. Applications for polypivalolactone include its use in making films (e.g., U.S. Pat. No. 3,476,714) and in making molded articles where high compressive strength, hardness, and high heat resistance are desirable. Mayne, in a paper entitled "The Polymerization of Polypivalolactone", published in Chemtech (December, 1972) points out the usefulness of polypivalolactone as an engineering thermoplastic because of its high heat resistance.
Notwithstanding the many desirable qualities of polypivalolactone (PPL), a problem associated with structural articles molded from PPL is their tendency to warp to an excessive extent. This problem occurs in articles molded by various methods known to the art, e.g., injection molding, compression molding, extrusion molding, blow molding, etc., and is especially troublesome when parts are molded with certain geometries (e.g., large, thin, rigid sections) and in configurations where uniformity and/or close tolerances are required. For these applications, low warpage in the finished part is a prime requisite.